Many motor vehicles, airplanes, helicopters, and ships are equipped with various optical sensors. Examples of optical sensors are camera systems, such as video cameras, night vision cameras, residual light amplifiers, or passive infrared detectors such as FLIR (forward looking infrared). The camera systems can use light in the ultraviolet (UV), visible (VIS), and infrared wavelength range (IR). Thus, they make it possible, even under poor weather conditions, such as darkness and fog, to precisely detect objects, motor vehicles, as well as persons. In motor vehicles, these camera systems can be placed behind the windshield inside the passenger compartment. Thus, they offer the capability of detecting hazardous situations and obstacles in a timely manner even in road traffic.
Other areas that use optical sensors include electronic distance measurement (EDM), for example, using laser distance meters. The distance to other motor vehicles can be determined. Such systems are common in the military field of application, but there are also many possibilities for civilian use. By measurements of the distance to the preceding vehicle, it is possible to determine the necessary safety distance and to significantly increase traffic safety. With automatic warning systems, the danger of a rear-end collision is significantly reduced.
Because of their sensitivity to weather influences or airstreams, such sensors must in all cases be protected by appropriate panes. The sensor can either be installed inside a motor vehicle or outside as in the case of thermal imaging cameras of helicopters. In that case, the sensor is installed in a pivotable housing outside on the helicopter. In order to ensure optimum functioning of the optical sensor, with both options, clean, condensation-free panes are absolutely essential. Condensation and icing significantly interfere with functioning, since they significantly reduce the transmission of electromagnetic radiation. Whereas wiper systems can be used for drops of water and dirt particles, these are usually inadequate with icing. Systems that heat the segment of the pane associated with the sensor at least briefly as needed and thus enable uninterrupted use are essential. In order to keep energy consumption and the voltage needed low, only the field of vision of the pane necessary for the sensor should be heated in this manner.
Besides the external surface of the pane, the inside pane must, above all, be kept free of condensation. So that no dirt and dust particles foul the sensors, the sensor and pane arrangement are usually encapsulated. If moisture penetrates into this encapsulated space, this moisture can, especially with cold outside temperatures, condense on the inside of the pane and restrict the functionality of the sensor.
DE 10 2007 001 080 A1 discloses an electrically heatable window pane. This is supplied with current using electrical bus bars and thus heated. The arrangement of the bus bars is such that only small electromagnetic fields are developed. Thus, operation of devices that react sensitively to electromagnetic fields is possible even in the region of the pane.
DE 101 56 850 A1 discloses a sensor in a motor vehicle window pane, whose lens is sealed off from the motor vehicle interior by encapsulation. This configuration prevents the deposition of dust particles on the lens. A particle filter is provided for air exchange.
DE 10 2004 054 161 A1 discloses an infrared light detection area in a motor vehicle windshield. The infrared light detection area is surrounded by heating elements that keep it ice and condensation free by heat conduction. EP 1 605 729 A2 discloses an electrically heatable pane with a camera window. This camera window is kept condensation and ice free by means of a heating device. The heating element is laminated into the pane at the position of the camera window. In addition, another additional heating element can be applied on the pane surface. The additional heating element is preferably printed onto the pane surface as a conductive paste.